The present invention relates to an ink jet recording head that is constructed so that it produces pressure fluctuations in ink in the pressure chamber by operations of a pressure generating element and ejects ink droplets through a nozzle orifice, a method for manufacturing the recording head, a method for driving the recording head, and an ink jet recording apparatus incorporating the recording head.
There are various types of ink jet recording heads that are used for an ink jet recording apparatus of a printer, plotter, etc., for example, types in which a piezoelectric vibrator or a heating element is used as a pressure generating element.
For example, in a recording head employing a piezoelectric vibrator, the ink pressure in the pressure chamber is varied by deforming a resilient plate, which partially sections the pressure chamber, through use of the piezoelectric vibrator, and ink droplets are ejected through the nozzle orifice by fluctuations in the ink pressure. Further, in a recording head employing a heating element, the heating element is provided in the pressure chamber, wherein ink is boiled by radically heating the heating element to cause air bubbles to be generated in the pressure chamber. And, the ink in the pressure chamber is pressurized by the air bubbles, and ink droplets are ejected through the nozzle orifice.
That is, either of these recording heads ejects ink droplets by varying the ink pressure in the pressure chamber.
In these types of recording heads, pressure vibrations are excited in the ink in the pressure chamber as if the inside of the pressure chamber operates like an acoustic tube in accordance with fluctuations in the ink pressure.
For example, in the recording head employing the piezoelectric vibrator, pressure vibrations having a natural period are excited, which is mainly determined by the thickness and/or area of the resilient plate, shape of the pressure chamber, compressibility of the ink, etc. Further, in the recording head employing the heating element, pressure vibrations having a natural period are excited, which is mainly determined by the shape of the pressure chamber, compressibility of the ink, etc.
And, in these types of recording heads, the ejection timing of ink droplets is established by the natural period of ink, and the recording heads are constructed so that the eject of ink droplets can be efficiently carried out.
However, in these types of recording heads, remarkably minute processing and assembling at the micrometer level (μm) are carried out. Therefore, the thickness and/or area of the resilient plate, shape of the pressure chamber, size of the nozzle orifice, etc., may change in respective recording heads, whereby the natural period of ink in the pressure chamber may vary. Therefore, if all the recording heads are driven by a drive signal having the same waveform, the eject characteristics of ink droplets may also vary in compliance with the unevenness of the natural period.
For example, as the natural period is deviated from the designed criterion (tolerance), the meniscus after ink droplets are ejected, that is, suppression of the vibration of the free surface of the ink, which is exposed at the nozzle orifice, becomes insufficient, and is not stabilized. In addition, an external force applied to the ink by operations of the pressure generating element is counterbalanced by the pressure vibrations in the ink.
For this reason, the amount of ink droplets that are subsequently ejected, (that is, the amount of ink), and the flying speed of ink droplets, (that is, the ink velocity), varies in respective recording heads.
As a result, there arises a problem in that the quality of recorded images becomes uneven in respective recording heads. Further, a recording head whose eject characteristics are greatly deviated from the designed criterion should be abolished, thereby reducing the yield ratio thereof.
In addition, it is considered that the natural period of ink in the pressure chamber is measured in respective assembled recording heads, and an attempt is made to make the image quality uniform by varying the waveform of the drive signal in response to the measured natural period. However, if a separate or independent waveform is established in respective recording heads, the cost of production will be worsened, wherein it would become difficult to carry out mass production in view of time and cost, etc.